This section is intended to provide a background or context to the disclosed embodiments. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
The performance of a wireless communication system is sometimes limited by interference between the various transmissions that occur within the wireless network. For example, the LTE system performance may be limited by inter-cell interference, especially near the cell edge regions where the transmissions to/from the devices in neighboring cells may interfere with the operations of devices in the current cell. In order to reduce and/or control inter-cell interference, an LTE system may employ uplink power control mechanisms, such as inter-cell interference coordination (ICIC), to improve the signal-to-interference in the uplink channel. An overload indicator is one mechanism that is used to facilitate uplink inter-cell coordination. The overload indicators are exchanged among the base stations (or eNodeBs) of a network and provide information on the uplink interference level experienced in one or more parts of the cell bandwidth. A cell receiving the overload indicator may reduce the interference generated on some of the resource blocks by, for example, adjusting the transmission scheduling strategy and, thereby, improving the interference experienced by the cell(s) that issued the overload indicator(s).
Release 8 of the LTE standard specifications contain provisions for sending the overload indicator to a neighboring eNodeB over the backhaul X2 interface. The overload indicator consists of one value per resource block (RB) on the uplink. The overload indicator may further be quantized to three levels that are indicative of the level of interference experienced by a neighbor eNodeB on a particular resource block. The overload indicator, according to the Release 8 of the LTE standard specifications, must be sent at most once every 20 ms.
The above-described utilization of the overload indicator requires an X2 connection between all neighboring eNodeBs. However, such a connection may not be available and/or feasible in many instances. In particular, an X2 connection between eNodeBs may not exist in initial deployments of the LTE systems. Further, even if an X2 connection is available, the latency associated with receiving an overload indicator from a neighboring cell and making subsequent scheduling and/or power adjustments may be too high. It is also likely that certain eNodeB's, such as Home eNodeBs (or HeNBs), will not have X2 connections with their neighboring cells. In fact, in a dense HeNB deployment, it may be quite challenging to support X2 connections between a macro eNodeB and all the HeNBs within its coverage. In addition, HeNB deployments can give rise to particularly severe interference conditions since a user equipment cannot always connect to its optimal serving cell.
Another drawback associated with the current overload indication mechanism is that an eNodeB's response to the overload indicator is not standardized. As such, interference control among neighboring eNodeBs that are associated with different vendors may not be possible, or may be ineffective. Such a situation is likely to happen in HeNBs, where having neighboring eNodeBs from different vendors is quite likely.
Further, the backhaul-based overload indicator signaling requires an eNodeB to be aware of the interference environment in order to implement an appropriate response to the received overload indicators. In particular, the eNodeB receiving the overload indicator has to be aware of the particular UE (if any) that is contributing to the excessive interference seen at the neighbor eNodeB. Such an awareness may not be sufficiently established in cases where the wireless channel environment undergoes substantial changes between successive measurement reports that are received by the eNodeB.